Children with cerebral palsy and other neurologic diseases often present with sialorrhea. Intraglandular botulinum neurotoxin is being increasingly reported to be clinically effective for the treatment of sialorrhea. This treatment is becoming more popular in recent years because of being less invasive than surgical procedures. In addition, fewer adverse effects have been documented compared with oral or topical anticholinergic medication. We report the first case in a child with cerebral palsy who developed serious acute sialadenitis with submandibular sialolithiasis after intraglandular botulinum neurotoxin injection for sialorrhea.